//
// Created by yewei on 2023/1/3.
//
#include <bits/stdc++.h>

using namespace std;

int main() {
    freopen("../input.txt", "r", stdin);
    int d=0,n=0;
    cin>>d>>n;
    double a[n],b[n];
    for(int i=0;i<n;i++) cin>>a[i]>>b[i];
    double max_time = 0;
    for(int i=0;i<n;i++){
        if((d-a[i])/b[i]>max_time) max_time = (d-a[i])/b[i];
    }
    printf("%.06lf",d/max_time);
}
